Heretofore, in the injection molding of foamed plastic articles, such as an automotive glove box door, a sprue has been formed in the pour opening once the foamable mixture has expanded into conformity with the mold surface, as may be seen in U.S. Pat. No. 4,133,858 to Hayakawa et al..
In other instances, the pour opening has been plugged, but in an inefficient manner, such that time consuming manual cleaning of the pour opening is required due to the manner in which the pour opening is plugged after the foamable mixture has been injected into the mold. For example, in the molding system shown and described in U.S. Pat. No. 3,642,392, to Vanderhagen, a hinged cover is provided with an external conical surface machined to match the internal surface of the pour opening. However, by virtue of being rotated in an arcuate path into the pour opening, the conical surface cannot scrape any foam formation from the inner surface of the pour opening, or prevent leakage of chemicals into the space between the surfaces of the pour opening and the conical surface during the foam reaction process.